Long QT syndrome (LQTS) is a cardiac disorder associated with ventricular arrhythmias and sudden death. It can be caused by genetic defects or as a side effect of drugs, in both cases involving impairment of the hERG potassium channel. Lahti et al. developed a model involving cardiomyocytes differentiated from human induced pluripotent stem cells (iPSCs) and tested whether LQTS-associated phenotypes could be detected in vitro. Surprisingly, iPSC-derived cardiomyocytes from an asymptomatic carrier of a HERG mutation have an abnormal phenotype. These findings could be applied to assess cellular defects of individuals with LQTS, and suggest that asymptomatic carriers of mutations affecting hERG function have an increased risk of being adversely affected by certain drugs. Page 220

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial Share Alike License (http://creativecommons.org/licenses/by-nc-sa/3.0), which permits unrestricted non-commercial use, distribution and reproduction in any medium provided that the original work is properly cited and all further distributions of the work or adaptation are subject to the same Creative Commons License terms.